1. Field of the Invention
The present invention relates generally to methods and systems for controlling the mass flow rate of a fluid, and more particularly to the operation of mass flow controllers.
2. Discussion of the Related Art
Many industrial processes require precise control of various process fluids. For example, in the semiconductor industries, mass flow controllers are used to precisely measure and control the amount of a process fluid that is introduced to a process chamber. The term fluid is used herein to describe any type of matter in any state that is capable of flow. It is to be understood that the term fluid applies to liquids, gases, and slurries comprising any combination of matter or substance to which controlled flow may be of interest.
However, as technology progresses, the semiconductor processes continue to get tighter and tighter as the design geometry continues to shrink. Processes now require very fast response time (¼ second or even faster), strong immunity to perturbation (e.g. inlet pressure fluctuation) and large turn down (i.e. smaller minimum controllable setpoint).
Current mass flow controllers utilizing proportional, integral, and derivative (PID) based control are reaching the limit of their capability. They also require extensive tuning to be able to perform in a wide range of conditions and reject a large range of perturbation. For instance, tuning needs to be done for each specific application (i.e., type of fluid and operating conditions). Moreover, complex algorithms are required to be able to adjust the P, I and D when conditions change.
To combat some of these problems, the disclosed embodiments include a system and method for using a model for improving control of a mass flow controller.